TT vs ST dyno overlay
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From: Atlanta, GA
Originally Posted by BriGuyMax
Actually I was talking about the exhaust stroke. When the rod is at an angle the piston is not changing direction. The direction change is what puts the most stress on the rod and it only happens at the top of the stroke or the bottom of the stroke when the rod is exactly perpendicular to the force being applied.
You are correct in that if a constant force is applied to the piston (with counterforce at the crank) then the most stress is when the rod is perpendicular to the piston, because at all other positions, some of that force is being opposed by the sidewall of the cylinder.
However, the force on the piston during combustion is many times what it is during any other point in the cycle, which overwhelms the reduction in stress to to the angle of the connection rod.
This is however, moot. The most stress on a rod would be in a binding situation (oil starved or turned journal), which creates a shear component to the stress, which will, in technical terms, f*** yo rods up, man.
Last edited by 03BrickyardZ; Dec 4, 2006 at 10:03 AM.
Originally Posted by captj3
The st may make more tq than hp, but the tt are more linear in there tq. They carry the tq to redline where the st's drop off like a brick.
Originally Posted by 03BrickyardZ
the most stress on a rod is going to be created at any moment that the force down on the piston (and up on the crank) is at a maximum, which would be during combustion.
You are correct in that if a constant force is applied to the piston (with counterforce at the crank) then the most stress is when the rod is perpendicular to the piston, because at all other positions, some of that force is being opposed by the sidewall of the cylinder.
However, the force on the piston during combustion is many times what it is during any other point in the cycle, which overwhelms the reduction in stress to to the angle of the connection rod.
This is however, moot. The most stress on a rod would be in a binding situation (oil starved or turned journal), which creates a shear component to the stress, which will, in technical terms, f*** yo rods up, man.
You are correct in that if a constant force is applied to the piston (with counterforce at the crank) then the most stress is when the rod is perpendicular to the piston, because at all other positions, some of that force is being opposed by the sidewall of the cylinder.
However, the force on the piston during combustion is many times what it is during any other point in the cycle, which overwhelms the reduction in stress to to the angle of the connection rod.
This is however, moot. The most stress on a rod would be in a binding situation (oil starved or turned journal), which creates a shear component to the stress, which will, in technical terms, f*** yo rods up, man.
Exactly, but my point was that it's not "power" that typically breaks rods. Excessive RPM and oil starvation are much more common factors in rod failure. Taurran claimed that that ST turbo setups are more likely to break rods because they produce more peak torque. I disagreed and I don't see how anything you have said counters what I said.
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Joined: Oct 2006
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From: Atlanta, GA
Originally Posted by BriGuyMax
Exactly, but my point was that it's not "power" that typically breaks rods. Excessive RPM and oil starvation are much more common factors in rod failure. Taurran claimed that that ST turbo setups are more likely to break rods because they produce more peak torque. I disagreed and I don't see how anything you have said counters what I said.
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